AMP deaminase (AMPDA) inhibitors increase the levels of extracellular adenosine and preserve intracellular adenylate pools in cellular models of ATP depletion and therefore represent a potential new class of antiischemic drugs. Recently we reported that replacement of the ribose 5'-monophosphate component of the very potent transition-state analogue AMPDA inhibitor coformycin monophosphate (1) with a simple alkylcarboxy group resulted in potent, selective, and cell-penetrating AMPDA inhibitors. Here we report that replacement of this alkylcarboxy group with an alpha-substituted alkylmalonic acid resulted in enhanced inhibitor potency. The lead compound, 3-(5, 5-dicarboxy-6-(3-(trifluoromethyl)phenyl)-n-hexyl)coformycin aglycon (21), exhibited an AMPDA K(i) of 0.029 microM which is (3 x 10(5))-fold lower than the K(M) for the natural substrate AMP. A comparison of inhibitory potencies shows that the diacid analogues with alpha-benzyl substituents are 2-10-fold more inhibitory than similar monoacid-monoester, monoester-monoamide, or diester derivatives. Finally, these diacid analogues are 2-40-fold more potent inhibitors than the corresponding monocarboxylates.